Optical information recording medium

ABSTRACT

An optical information recording medium which is capable of performing high-density recording of record data, and storing the recorded data for a long time period such that the recorded data can be normally reproduced during the long time period. An optical information recording medium has a recording layer formed on a substrate, for having a laser beam irradiated thereto for recording and reproduction of record data. The recording layer includes a first sub-recording film and a second sub-recording film. The first sub-recording film is formed of a first material containing Si as the main component. The second sub-recording film is formed of a second material containing Cu as the main component and having Mg added thereto, and disposed in the vicinity of the first recording film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical information recording mediumconfigured to be capable of recording and reproducing record data byirradiating a laser beam to a recording layer formed on a substrate.

2. Description of the Related Art

As an optical information recording medium of this kind, a write-onceoptical information recording medium has been conventionally proposedwhich includes a recording layer formed of an organic dye-based materialand has the optical characteristics of the recording layer changed as alaser beam is irradiated thereon. Meanwhile, in recent years, opticalinformation-recording media are desired to have the capability ofrecording and reproducing a large amount of record data at a high speed(in a short time period). Accordingly, the optical information recordingmedium of the above-mentioned kind is required to enhance recordingdensity of record data, and to meet the requirement, the diameter of abeam spot of a laser beam used for recording or reproduction of recorddata tends to be reduced. More specifically, record data are recordedand reproduced using a pickup which is equipped with an objective lenshaving a numerical aperture (NA) of not less than 0.7 (e.g. a numericalaperture (NA) of approximately 0.85), and is capable of emitting a laserbeam having a wavelength (λ) of not more than 450 nm (e.g. a wavelength(λ) of approximately 405 nm). However, when a recording layer is formedby an organic dye-based material, it is difficult to change the opticalcharacteristics of the recording layer using a laser beam with awavelength of 405 nm or so. Therefore, the optical information recordingmedium including a recording layer formed of an organic dye-basedmaterial suffers from the problem that it has difficulty in performinghigh-density recording for enabling a large amount of record data to berecorded and reproduced at a high speed.

On the other hand, an optical disk is disclosed in Japanese Laid-OpenPatent Publication No. S62-204442, which includes a recording layercapable of recording record data thereon by a phase change to acrystalline state or an amorphous state which is caused by irradiationof a laser beam thereon. This optical disk is comprised of a protectivefilm, a recording layer, a protective film, and a protective film,sequentially deposited on a substrate in the mentioned order. In thiscase, the protective films deposited in a manner sandwiching therecording layer are provided for preventing the recording layer fromflying off or being bored during irradiation of the laser beam (duringrecording of record data), and made of SiO, SiO₂, SiN₃, or the like.Further, the recording layer is formed by depositing two recording filmsformed of respective materials different from each other. Morespecifically, for example, one of the recording films is made of Si orTe, and the other is made of Au, Ag, or Ge.

For example, when the one of the recording films is made of Si, and theother is made of Au, both of the recording films are mixed with eachother by being irradiated with the laser beam, whereby a single layer ofAuSi is formed. In this case, to form the recording layer such that itis changed to a crystalline state or an amorphous state according to theirradiation power and irradiation time period of the laser beam, it isrequired that the atomic percentage of Si to the whole single layer ofAuSi is within a range of 20 at % to 30 at %. Therefore, in the proposedoptical disk, the recording films are formed by defining the ratiobetween the thickness of the one recording film and that of the other tobe within a range of 2:8 to 3:7, whereby the atomic percentage of Si tothe whole single layer of AuSi is caused to be within the above range.The uppermost protective film, which is the uppermost layer, preventsthe other two protective films and the recording layer from beingscratched, and is in the form of a thin film made of anultraviolet-curing resin such that it covers the protective filmimmediately thereunder. Differently from an optical informationrecording medium having a recording film formed of an organic dye-basedmaterial, the above optical disk is capable of recording and reproducingrecord data using a laser beam having a relatively short wavelength.Therefore, with this optical disk, it is possible to performhigh-density recording using a laser beam which is small in the diameterof a beam spot thereof.

However, as a result of the study of the above prior art, the presentinventors have found the following problems: In the conventional opticaldisk, the recording layer is selectively changed to a crystalline stateor an amorphous state by adjusting the irradiation power and irradiationtime period of the laser beam, whereby the optical characteristics ofthe recording layer are changed. In this case, if the optical disk whoserecording layer has been changed into a single layer of AuSi by beingirradiated with the laser beam (i.e. which has record data recorded onthe recording layer) is left standing for a long time period, the levelof noise in a reproduction signal is progressively increased to decreasethe C/N ratio of the reproduction signal, whereby it becomes difficultto normally reproduce the recorded data. Further, if the optical desk isleft standing for a long time period, the reflectance of the recordinglayer exhibited with respect to the laser beam is decreased to decreasethe C/N ratio of the reproduction signal. This makes it difficult tonormally reproduce the recorded data. As described above, theconventional optical disk suffers from the problems of a large degree ofdeterioration caused by aging with respect to the noise level(hereinafter also referred to as “degree of noise-causingdeterioration”) and a large degradation ratio of reflectance of thelaser beam L, which makes it difficult for the conventional optical diskto store record data for a long time period such that the record datacan be normally reproduced during the long time period.

SUMMARY OF THE INVENTION

The present invention has been made to solve the problems describedabove, and a main object thereof is to provide an optical informationrecording medium which is capable of performing high-density recordingof record data, and storing the recorded data for a long time periodsuch that the recorded data can be normally reproduced during the longtime period.

To attain the above object, the present invention provides an opticalinformation recording medium for recording and reproducing record data,comprising a substrate, and a recording layer formed on the substrate,for having a laser beam irradiated thereto for recording andreproduction of the record data, the recording layer including a firstrecording film formed of a first material containing Si as a maincomponent, and a second recording film formed of a second materialcontaining Cu as a main component and having Mg added thereto, thesecond recording film being formed in the vicinity of the firstrecording film. It should be noted that in the present invention, theterm “main component” is intended to mean a component which has thelargest composition ratio (at %: atomic percentage) of a plurality ofelements constituting a material for forming a film or a layer.

With the arrangement of this optical information recording medium, thefirst recording film is formed by using the first material containing Sias the main component, and the second recording film is formed in thevicinity of the first recording film by using a second materialcontaining Cu as the main component and having Mg added thereto. Theaddition of Mg makes it possible to reduce the degree of noise-causingdeterioration (suppress a rise in the noise level due to aging), andgreatly improve the degradation ratio of reflectance (suppress adecrease in reflectance). Consequently, it becomes possible to performhigh-density recording of record data, and store the recorded data for along time period such that the recorded data can be normally reproducedduring the long time period. Further, the addition of Mg makes itpossible to improve the smoothness of the surface of the secondrecording film, thereby significantly lowering the noise level.Therefore, the C/N ratio can be enhanced, whereby record data can bereliably reproduced. Furthermore, recorded portions (pits) can bepositively formed in the recording layer even when a laser beamrelatively small in power is irradiated.

Preferably, the second material has Mg added thereto in an amount notless than 5 at % and less than 50 at %. With this arrangement of thepreferred embodiment, it is possible to decrease the degree ofnoise-causing deterioration and reduce the degradation ratio ofreflectance. This makes it possible to provide an optical informationrecording medium capable of reliably storing record data for a long timeperiod.

More preferably, the second material has Mg added thereto in an amountnot less than 15 at % and less than 50 at %. With this arrangement ofthe preferred embodiment, it is possible to further reduce thedegradation ratio of reflectance. Therefore, an optical informationrecording medium can be provided which is capable of more reliablystoring record data for a long time period.

Preferably, the recording layer is configured such that the first andsecond recording films are in contact with each other. With thisarrangement of the preferred embodiment, when the laser beam adjusted toa recording power is irradiated to the recording layer, the first andsecond recording films can be easily mixed with each other to therebyform the recorded portions.

Preferably, the optical information recording medium includes aprotective layer formed in a manner covering the recording layer. Withthis arrangement of the preferred embodiment, it is possible topositively prevent the first dielectric layer, the recording layer, andso forth, from being scratched. Further, since corrosion of therecording layer can be prevented, it is possible to store recorded datafor a long time period such that the recorded data can be normallyreproduced during the long time period.

More preferably, the protective layer is formed to be capable oftransmitting the laser beam therethrough, the recording layer beingformed by the second recording film and the first recording film,sequentially deposited on the substrate in the mentioned order, and theoptical information recording medium is configured such that the recorddata can be recorded and reproduced by irradiation of the laser beam tothe recording layer from a protective layer side. With this arrangementof the preferred embodiment, the protective layer can be formed to havea thickness less than that of the substrate, so that even when a pickuphaving an objective lens with a large numerical aperture (NA) is used, asufficiently large tilt margin can be secured. Further, in theconstruction adapted to irradiation of the laser beam to the recordinglayer from the protective layer side, the present optical informationrecoding medium can more reliably form the recorded portions in therecording layer even with a laser beam relatively small in power, thanan optical information recording medium in which the recording layer isformed by the first recording film and the second recording film,sequentially deposited on the substrate in the mentioned order.

Further preferably, the optical information recording medium includes afirst dielectric layer formed between the recording layer and theprotective layer, and a second dielectric layer formed between thesubstrate and the recording layer. With this arrangement of thepreferred embodiment, it is possible to prevent thermal deformations ofthe substrate and the protective layer during irradiation of the laserbeam (during formation of the recorded portions). As a result, it ispossible to positively prevent a rise in the noise level caused by thethermal deformations.

Even more preferably, the optical information recording medium includesa reflective layer formed between the substrate and the seconddielectric layer. With this arrangement of the preferred embodiment,since the effect of multi-beam interference is further increased, it ispossible to further increase the difference in optical reflectancebetween the recorded portions and the unrecorded portions, wherebyrecorded data can be more reliably reproduced.

Preferably, the substrate is formed to be capable of transmitting thelaser beam therethrough, the recording layer being formed by the firstrecording film and the second recording film, sequentially deposited onthe substrate in the mentioned order, and the optical informationrecording medium is configured such that the record data can be recordedand reproduced by irradiation of the laser beam to the recording layerfrom a substrate side. With this arrangement of the preferredembodiment, since the second recording film is formed by using thematerial having Mg added thereto, it is possible to reduce the degree ofnoise-causing deterioration (suppress a rise in the noise level due toaging), and greatly improve the degradation ratio of reflectance(suppress a decrease in reflectance). Consequently, it is possible tostore record data for a long time period. In this case, in theconstruction adapted to irradiation of the laser beam to the recordinglayer from the substrate side, since the first recording film and thesecond recording film are sequentially deposited on the substrate in thementioned order, the recorded portions can be more reliably formed inthe recording layer even with a laser beam relatively small in power,than when the recording layer is formed by the second recording film andthe first recording film, sequentially deposited on the substrate in thementioned order.

More preferably, the optical information recording medium includes aprotective layer formed in a manner covering the recording layer, afirst dielectric layer formed between the substrate and the recordinglayer, and a second dielectric layer formed between the recording layerand the protective layer. The substrate is formed to be capable oftransmitting the laser beam therethrough, the recording layer beingformed by the first recording film and the second recording film,sequentially deposited on the substrate in the mentioned order, and theoptical information recording medium is configured such that the recorddata can be recorded and reproduced by irradiation of the laser beam tothe recording layer from a substrate side. With this arrangement of thepreferred embodiment, it is possible to prevent thermal deformations ofthe substrate and the like during irradiation of the laser beam (duringformation of the recorded portions). As a result, it is possible topositively prevent a rise in the noise level caused by the thermaldeformations.

Further preferably, the optical information recording medium includes areflective layer formed between the second dielectric layer and theprotective layer. With this arrangement of the preferred embodiment,since the effect of multi-beam interference is further increased, it ispossible to further increase the difference in optical reflectancebetween the recorded portions and the unrecorded portions, wherebyrecord data can be more reliably reproduced.

It should be noted that the present disclosure relates to the subjectmatter included in Japanese Patent Application No. 2003-208547 filed onAug. 25, 2003, and it is apparent that all the disclosures therein areincorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will beexplained in more detail below with reference to the attached drawings,wherein:

FIG. 1 is a cross-sectional view showing the construction of an opticalinformation recording medium according to an embodiment of the presentinvention;

FIG. 2 is a characteristics diagram showing the relationship between theamount of Mg added to a material for forming a second sub-recordingfilm, and the degree of noise-causing deterioration;

FIG. 3 is a characteristics diagram showing the relationship between theamount of Mg added to a material for forming the second sub-recordingfilm, and the degradation ratio of reflectance; and

FIG. 4 is a cross-sectional view showing the construction of an opticalinformation recording medium according to another embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will now be described in detail with reference to theaccompanying drawings showing a preferred embodiment thereof.

First, a description will be given of the construction of an opticalinformation recording medium 1 according to the present invention.

The optical information recording medium 1 is a single-sidedsingle-layered optical disk of a write-once type, having an outerdiameter of approximately 120 mm and a thickness of 1.2 mm, andconfigured to be capable of recording and reproducing record data, usinga blue-violet laser beam (hereinafter referred to as the “laser beam”) Lhaving a wavelength (λ) not less than 380 nm and not more than 450 nm(e.g. 405 nm), emitted from an objective lens having a numericalaperture (NA) of not less than 0.7 (e.g. approximately 0.85). Morespecifically, as shown in FIG. 1, the optical information recordingmedium 1 is comprised of a reflective layer 3, a second dielectric layer5 b, a recording layer 4, a first dielectric layer 5 a, and a lighttransmitting layer 6, sequentially deposited on a substrate 2 in thementioned order. Further, the optical information recording medium 1 hasa central portion thereof formed with a central hole for mounting(clamping) the same on a recording/reproducing apparatus.

The substrate 2 is in the form of a disk with a thickness ofapproximately 1.1 mm, made e.g. of a polycarbonate resin by theinjection molding method. In this case, the substrate 2 can also beformed by any suitable one of various substrate-forming methods, such asthe 2P method. Further, one surface (upper surface as viewed in FIG. 1)of the substrate 2 is formed with grooves and lands extending helicallyfrom a central portion of the substrate 2 toward the outer peripherythereof. In this case, the grooves and the lands function as guidetracks for recording and reproducing data on and from the recordinglayer 4. Therefore, to enable accurate tracking to be performed, it ispreferable to form grooves between the lands, for example, such thatthey have a depth not less than 10 nm and not more than 40 nm, and apitch not less than 0.2 μm and not more than 0.4 μm. Further, theoptical information recording medium 1 is configured such that the laserbeam L is to be irradiated thereon from the light transmitting layer 6side when data is recorded or reproduced. Therefore, the substrate 2 isnot required to have a light transmitting property, i.e. be transparent,so that the optical information recording medium 1 has more options forselecting materials for forming the substrate 2 than the existinggeneral optical information recording media (e.g. CD-R). Morespecifically, the material for forming the substrate 2 is not limited tothe above-mentioned polycarbonate resin, but resin materials, such as anolefin resin, an acrylic resin, an epoxy resin, a polystyrene resin, apolyethylene resin, a polypropylene resin, a silicone resin, afluorocarbon resin, an ABS resin, and an urethane resin, as well asglass and ceramic materials can be employed as the substrate-formingmaterial. However, it is preferable to employ one of the resin materialsthat are easy to mold and relatively inexpensive, such as thepolycarbonate resin and the olefin resin.

The reflective layer 3 reflects the laser beam L irradiated thereon viathe light transmitting layer 6 when recorded data is reproduced, and ismade of any of metal materials, such as Mg, Al, Ti, Cr, Fe, Co, Ni, Cu,Zn, Ge, Ag, Pt, and Au, or alloys containing selected ones of them (e.g.AgNdCu=98:1:1, and AgPdCu=98:1:1) such that it has a thickness not lessthan 10 nm and not more than 300 nm. In this case, to reflect thenecessary and sufficient amount of the laser beam L, it is preferable todefine the thickness of the reflective layer 3 to be not less than 20 nmand not more than 200 nm (e.g. 100 nm). Further, metal materials, suchas, Al, Au, Ag, Cu, and the metal materials such as an alloy of Ag andCu, have a high reflectance, and therefore it is preferable to use ametal material containing at least one of these metals as the materialfor forming the reflective layer 3.

The first dielectric layer 5 a and the second dielectric layer 5 b (alsoreferred to as the “dielectric layers 5” when they are not distinguishedfrom each other) correspond to first and second dielectric layers in thepresent invention, respectively, and are formed such that they sandwichthe recording layer 4. The dielectric layers 5 prevent (reduce)corrosion of the recording layer 4, thereby preventing degradation ofrecorded data, and at the same time prevent thermal deformations of thesubstrate 2 and the light transmitting layer 6 during recording ofrecord data to thereby prevent deterioration of jitter characteristics.Further, the dielectric layers 5 also serve to increase the amount ofchange in the optical characteristics between recorded portions havingrecord data recorded thereon (portions of the recording layer, havingpits formed thereon) and unrecorded portions having no record datarecorded thereon (portions of the recording layer, having no pits formedthereon) by the effect of multi-beam interference. In this case, toincrease the amount of change in the optical characteristics, it ispreferable to form the dielectric layers 5 using a dielectric materialhaving a high index of refraction (n) in the wavelength region of thelaser beam L. Further, when the laser beam L is irradiated, if anexcessively large amount of energy is absorbed by the dielectric layers5, recording sensitivity of the recording layer 4 is reduced. Therefore,it is preferred to form the dielectric layers 5 using a dielectricmaterial having a small extinction coefficient (k) in the wavelengthregion of the laser beam L to thereby prevent the reduction of therecording sensitivity.

More specifically, from the viewpoint of prevention of thermaldeformations of the substrate 2 and the light transmitting layer 6, andenhancement of protecting characteristics of the dielectric layers 5 forprotecting the recording layer 4 as well as obtaining the sufficienteffect of multi-beam interference, it is preferable to employ adielectric material having a light transmitting property, such as any ofAl₂O₃, AlN, ZnO, ZnS, GeN, GeCrN, CeO₂, SiO, SiO₂, Si₃N₄, SiC, La₂O₃,TaO, TiO₂, SiAlON (mixture of SiO₂, Al₂O₃, Si₃N₄, and AlN), and LaSiON(mixture of La₂O₃, SiO₂, and Si₃N₄), any of oxides, nitrides, sulfides,and carbides of Al, Si, Ce, Ti, Zn, and Ta, and mixtures thereof, as thedielectric material for forming the dielectric layers 5. In this case,the first dielectric layer 5 a and the second dielectric layer 5 b canbe formed of the same dielectric material, or alternatively ofrespective dielectric materials different from each other. Further, oneor both of the first dielectric layer 5 a and the second dielectriclayer 5 b can be configured to have a multilayer structure formed by aplurality of dielectric layers.

In the optical information recording medium 1 according to the presentinvention, the first dielectric layer 5 a and the second dielectriclayer 5 b are formed of a dielectric material mainly composed of amixture of ZnS and SiO₂ (preferably, molar ratio of ZnS:SiO₂=80:20),such that they have a thickness not less than 10 nm and not more than200 nm (e.g. 25 nm). In this case, the mixture of ZnS and SiO₂ has ahigh index of refraction (n), and a relatively small extinctioncoefficient (k) with respect to the laser beam L in the wavelengthregion ranging from 380 nm to 450 nm inclusive, which causes a moreconspicuous change in optical characteristics of the recording layer 4before and after recording of data thereon, and at the same timeprevents the recording sensitivity of the same from being degraded.Further, the thickness of each of the first and second dielectric layers5 a and 5 b is not limited to the examples described above, but when thedielectric layer has a thickness of less than 10 nm, it is difficult toobtain the aforementioned effects. Inversely, when the dielectric layerhas a thickness of more than 200 nm, it takes a long time to deposit thedielectric layer, which can sharply increase the manufacturing costs ofthe optical information recording medium 1, and further cause cracks inthe optical information recording medium 1 due to internal stress of thefirst dielectric layer 5 a or the second dielectric layer 5 b.Therefore, it is preferable to define the thicknesses of the first andsecond dielectric layers 5 a and 5 b to be not less than 10 nm and notmore than 200 nm.

The recording layer 4 has optical characteristics thereof changed by thelaser beam L irradiated thereto during recording of record data so as tobe formed with recorded portions M (pits). The recording layer 4 isformed by two thin films, i.e. a second sub-recording film 4 b and afirst sub-recording film 4 a, sequentially deposited on the substrate 2in the mentioned order. In this case, the recording layer 4 is formedsuch that the two thin films are deposited in the order of the firstsub-recording film 4 a and the second sub-recording film 4 b from thelight transmitting layer 6 side (side closer to the incidence plane ofthe laser beam L). This enables the optical characteristics of therecording layer 4 to be sufficiently changed even with a laser beam Lrelatively small in power, thereby making it possible to reliably formthe recorded portions M. The first sub-recording film 4 a corresponds toa first recording film according to the present invention, and is in theform of a thin film made of a material (first material in the presentinvention) containing Si as the main component. By forming the firstsub-recording film 4 a using the material containing Si as the maincomponent, it is possible to fully enhance the C/N ratio of areproduction signal, as will be described hereinafter. In the embodimentof the present invention, the atomic percentage of Si to the wholematerial for forming the first sub-recording film 4 a is defined to benot lower than 95 at % (e.g. 99 at %).

Further, the second sub-recording film 4 b corresponds to a secondrecording film according to the present invention, and is in the form ofa thin film made of a material (second material in the presentinvention) containing Cu as the main component and having Mg addedthereto. In this case, by forming the second sub-recording film 4 busing the material containing Cu as the main component, Cu as the maincomponent of the second sub-recording film 4 b and Si as the maincomponent of the first sub-recording film 4 a are rapidly mixed witheach other when the laser beam L is irradiated during recording ofrecord data. This makes it possible to promptly form recorded portions M(promptly record data). Further, the second sub-recording film 4 b isdeposited by using the material containing Cu as the main component, bythe vapor phase growth method, such as the vacuum deposition method andthe sputtering method, thereby making it possible to improve thesmoothness of the upper surface of the second sub-recording film 4 b.Furthermore, since Cu is a very inexpensive material, it is possible tofully reduce the manufacturing costs of the optical informationrecording medium 1.

In this case, when the second sub-recording film 4 b is formed of amaterial obtained by adding Mg to Cu, the smoothness of the uppersurface of the second sub-recording film 4 b can be further increasedcompared with that of the upper surface of the second sub-recording film4 b formed of a material made of only Cu (having no Mg added thereto).This makes it possible to decrease the noise level of the reproductionsignal to increase the C/N ratio. Further, the use of the materialobtained by adding Mg to Cu makes it possible to suppress thedegradation of reflectance of the second sub-recording film 4 b, whichenables record data to be stored for a long time period. Additionally,since both Cu and Mg are pollution-free materials, it is possible tominimize impact on a terrestrial environment, e.g. even if used opticalinformation recording media 1 are buried in the earth for disposal. Inthis case, it is preferred to use a material having Mg added in anamount not less than 1 at % and less than 50 at %, as the material forforming the second sub-recording film 4 b. Further, to decrease thedegree of noise-causing deterioration of the medium 1 and reduce thedegradation ratio of reflectance of the second sub-recording film 4 b,it is preferred to use a material having Mg added in an amount not lessthan 5 at % and less than 50 at %. Moreover, to further reduce thedegradation ratio of reflectance of the second sub-recording film 4 b,it is preferred to use a material having Mg added in an amount not lessthan 15 at % and less than 50 at %. In the embodiment of the presentinvention, for example, the atomic percentage of Cu to the wholematerial for forming the second sub-recording film 4 b is defined to be80 at %, and that of Mg, which is added, to the same is defined to be 20at %.

As the thickness of the first sub-recording film 4 a and that of thesecond sub-recording film 4 b (the total thickness of the recordinglayer 4) are increased, the smoothness of the upper surface of the firstsub-recording film 4 a located closer to the incidence plane of thelaser beam L is reduced to cause an increase in the noise level of thereproduction signal and degrade the recording sensitivity of therecording layer 4. In this case, when the thickness of the recordinglayer 4 exceeds 50 nm, the recording sensitivity thereof is so reducedthat it can be difficult to use the medium 1 as the optical informationrecording medium. Meanwhile, when the total thickness of the recordinglayer 4 is less than 2 nm, the amount of change in opticalcharacteristics of the recording layer 4 before and after recording ofdata thereon is decreased to decrease the C/N ratio, which makes itdifficult to normally reproduce recorded data. Therefore, preferably,the total thickness of the recording layer 4 is defined to be not lessthan 2 nm and not more than 50 nm, and more preferably, it is defined tobe not less than 2 nm and not more than 30 nm. In this case, to decreasethe level of noise contained in the reproduction signal, the degree ofnoise-causing deterioration of the medium 1, and the degradation ratioof reflectance, it is preferable to form the sub-recording films 4 a and4 b such that the total thickness of the recording layer 4 is not lessthan 5 nm and not more than 15 nm.

Although the respective thicknesses of the sub-recording films 4 a and 4b are not particularly limited, to fully improve the recordingsensitivity of the recording layer 4, and at the same time sufficientlychange the optical characteristics of the recording layer 4 before andafter recording of data thereon, it is preferable to form thesub-recording films 4 a and 4 b such that each of them has a thicknessnot less than 2 nm and not more than 30 nm. Further, to moresufficiently change the optical characteristics of the recording layer 4before and after recording of data thereon, it is preferable to definethe respective thicknesses of the sub-recording films 4 a and 4 b suchthat the ratio between the thickness of the first sub-recording film 4 aand that of the second sub-recording film 4 b (thickness of the firstsub-recording film 4 a/thickness of the second sub-recording film 4 b)is not less than 0.2 and not more than 5.0. In the embodiment of thepresent invention, the recording layer 4 is formed, for example, suchthat the total thickness thereof becomes equal to 10 nm by defining thethickness of the first sub-recording film 4 a to be 5 nm, and that ofthe second sub-recording film 4 b to be 5 nm.

The light transmitting layer 6, which corresponds to a protective layerin the present invention, functions as an optical path of the laser beamwhen data is recorded or reproduced, and at the same time physicallyprotects the recording layer 4 and the first dielectric layer 5 a. Thelight transmitting layer 6 is formed of a resin material, such as anultraviolet-curing resin or an electron beam-curing resin, such that ithas a thickness not less than 1 μm and not more than 200 μm (preferably,not less than 50 μm and not more than 150 μm: e.g. 100 μm). In thiscase, when the light transmitting layer 6 has a thickness of less than 1μm, it becomes difficult to protect the recording layer 4 and the firstdielectric layer 5 a, whereas when the light transmitting layer 6 has athickness of more than 200 μm, it becomes difficult to form a lighttransmitting layer 6 whose parts (particularly, parts in the radialdirection) have a uniform thickness. Further, when the thick lighttransmitting layer 6 is formed of a material different from the materialfor forming the substrate 2, warpage of the optical informationrecording medium 1 can be caused by thermal expansion, thermalshrinkage, or the like thereof. It should be noted that the method offorming the light transmitting layer 6 includes a method of applying aresin material (on the first dielectric layer 5 a) by the spin coatingmethod or the like, and then curing the same, a method of affixing asheet material formed of a light-transmitting resin to the firstdielectric layer 5 a by an adhesive or the like. However, to preventattenuation of the laser beam L, it is preferable to employ the spincoating method which does not add the adhesive layer in the medium 1.

When the optical information recording medium 1 is manufactured, first,a stamper for molding a substrate is set in a mold mounted to aninjection molder. Then, the temperature of a polycarbonate resin, andthe temperature of the mold are set to approximately 360 degree Celsiusand approximately 120 degree Celsius, respectively, and at the sametime, other molding conditions, such as a clamping force, a cooling timeperiod, and the like, are set. The substrate 2 is formed by injectionmolding under these conditions. Then, the reflective layer 3 having athickness of approximately 100 nm is formed on the upper surface of thesubstrate 2 by the vapor phase growth method (the vacuum depositionmethod, the sputtering method, or the like: in the present case, e.g.the sputtering method) using chemical species containing Ag as the maincomponent. Next, the second dielectric layer 5 b having a thickness ofapproximately 25 nm is formed by the vapor phase growth method usingchemical species mainly composed of a mixture of ZnS and SiO₂ in amanner covering the reflective layer 3. Then, the second sub-recordingfilm 4 b having a thickness of approximately 5 nm is formed by the vaporphase growth method using the material (chemical species) containing Cuas the main component and having Mg added thereto, in a manner coveringthe second dielectric layer 5 b. Since the second sub-recording film 4 bis formed by using the material obtained by adding Mg to the maincomponent of Cu which is capable of ensuring the smoothness of the uppersurface of the second sub-recording film 4 b by itself, the uppersurface of the second sub-recording film 4 b is made even flatter orsmoother (the smoothness of the upper surface of the secondsub-recording film 4 b is ensured), compared with a case where amaterial having no Mg added thereto is used.

Then, the first sub-recording film 4 a having a thickness ofapproximately 5 nm is formed by the vapor phase growth method using thematerial (chemical species) containing Si as the main component in amanner covering the second sub-recording film 4 b. In forming the firstsub-recording film 4 a, since the upper surface of the secondsub-recording film 4 b has been formed flat, the upper surface of thefirst sub-recording film 4 a is also formed flat similarly to the uppersurface of the second sub-recording film 4 b. After that, the firstdielectric layer 5 a having a thickness of approximately 25 nm is formedby the vapor phase growth method using chemical species mainly composedof a mixture of ZnS and SiO₂, in a manner covering the firstsub-recording film 4 a. It should be noted that it is preferable to formthe reflective layer 3, the second dielectric layer 5 b, the secondsub-recording film 4 b, the first sub-recording film 4 a, and the firstdielectric layer 5 a, successively on the substrate 2 by using asputtering machine having a plurality of sputtering chambers, byadjusting layer-forming conditions on a chamber-by-chamber basis asrequired. Subsequently, the light transmitting layer 6 having athickness of approximately 100 μm is formed on the first dielectriclayer 5 a by applying e.g. an acrylic-based ultraviolet-curing resin (oran epoxy-based ultraviolet-curing resin) in a manner covering the firstdielectric layer 5 a by the spin coating method, and then curing thesame. In forming the light transmitting layer 6, conditions for spincoating (rotational speed, rate of change in the speed, a time periodtaken until the rotation is stopped, etc.) are adjusted, as required, soas to form the layer 6 such that it has a uniform thickness(particularly, in the radial direction). Further, to form the lighttransmitting layer 6 having a thickness of approximately 100 μm, it ispreferable to use a resin material (an ultraviolet-curing resin, in thepresent case) whose viscosity is high to some extent. Thus, the opticalinformation recording medium 1 is completed.

Next, the principles of recording of record data by the opticalinformation recording medium 1 will be described with reference todrawings.

First, the laser beam L adjusted to a recording power (e.g. ofapproximately 5.0 mW at the upper surface of the light transmittinglayer 6), having a wavelength (λ) of 405 nm, is emitted from anobjective lens having a numerical aperture (NA) of 0.85, and irradiatedonto the optical information recording medium 1. At this time, in anarea of the recording layer 4 to which the laser beam L is irradiated,an element (Si, in the present case), which is the main component of thefirst sub-recording film 4 a, and an element (Cu, in the present case),which is the main component of the second sub-recording film 4 b, aremixed with each other, to form the recorded portions M (only one ofwhich is shown in FIG. 1). It should be noted that although FIG. 1 showsa state of the area irradiated with the laser beam L, in which the firstsub-recoding film 4 a and the second sub-recording film 4 b are totallymixed in the direction of thickness to form the recoded portions M, itis also possible to form the recorded portions M such that record datacan be normally reproduced therefrom (such that the record data issufficiently readable), even if the first and second sub-recording films4 a and 4 b are partially mixed with each other in the vicinity of theinterface therebetween. In this case, the portions remaining in thestate of the first sub-recording film 4 a and the second sub-recordingfilm 4 b being layered (hereinafter also referred to as the “layeredportions” or “unrecorded portions”), and the recorded portions M arelargely different in optical characteristics. Hence, when the laser beamL adjusted to a reproduction power is irradiated to the layered portionand the recorded portions M, respective values of reflectance exhibitedby the two kinds of portions are very different from each other.Therefore, by detecting the difference in the reflectance, it isdetermined whether or not each recorded portion M exists, and based onthe determination, the recording/reproducing apparatus reproduces(reads) record data.

In this case, in the optical information recording medium 1, since thesecond sub-recording film 4 b is formed of the material containing Cu asthe main component and having Mg added thereto, the smoothness of theupper surface of the second sub-recording film 4 b is improved comparedwith a second sub-recording film 4 b made of a material having no Mgadded thereto, and hence even if the diameter of a beam spot of thelaser beam L is made very small, it is possible to positively form therecorded portions M. Further, since the smoothness of the upper surfaceof the second sub-recording film 4 b is improved by addition of Mg, thenoise level of the reproduction signal is prevented from rising.Furthermore, since the second sub-recording film 4 b and the firstsub-recording film 4 a are sequentially formed on the substrate 2 in thementioned order, Cu (the second sub-recording film 4 b formed of thematerial containing Cu as the main component) having a higher opticalreflectance is located on the far side in the direction of irradiationof the laser beam L, so that the recorded portions M can be morereliably formed in the recording layer 4 even with the laser beam Lsmall in power, than when the recording layer 4 is formed by the firstsub-recording film 4 a and the second sub-recording film 4 b,sequentially deposited on the substrate 2 in the mentioned order.

Further, the recording layer 4 is sandwiched by the first dielectriclayer 5 a and the second dielectric layer 5 b, and hence even when thefirst sub-recording film 4 a and the second sub-recording film 4 b areheated by the irradiation of the laser beam L to the extent that theyare mixed with each other, it is possible to prevent thermaldeformations of the substrate 2 and the light transmitting layer 6. Thismakes it possible to prevent a rise in the noise level, a decrease inthe C/N ratio, and deterioration of jitter characteristics. Furthermore,since the first sub-recording film 4 a is made of the materialcontaining Si as the main component, and the second sub-recording film 4b is made of the material containing Cu as the main component, it ispossible to sufficiently change the optical characteristics of portionsof the recording layer 4, which are formed into the recorded portions M,before and after recording of record data thereon. As a result, it canbe positively detected whether or not each recorded portion M exists,thereby making it possible to reliably reproduce record data.

Next, the relationship between the amount of Mg added to the material(material containing Cu as the main component) for forming the secondsub-recording film 4 b, and the degree of noise-causing deteriorationand the degradation ratio of reflectance will be described withreference to FIGS. 2 and 3.

As described hereinbefore, if Mg is added to the material (materialcontaining Cu as the main component) for forming the secondsub-recording film 4 b, it is possible to improve the smoothness of theupper surface of the second sub-recording film 4 b formed by the vaporphase growth method. Therefore, it is possible to decrease the level ofnoise contained in the reproduction signal (noise level of thereproduction signal). In this case, the present inventors have confirmedthat the noise level at least in a frequency band of 4.1 MHz to 16.5 MHzis reduced by addition of Mg. Further, the degree of noise-causingdeterioration can be decreased by adding Mg to the material used forforming the second sub-recording film 4 b, thereby making it possible tostore record data for a long time period. More specifically, the opticalinformation recording medium 1 was left standing e.g. for 50 hours in anenvironment of 80 degree Celsius and 85% RH, while measuring the noiselevel before and after causing the medium 1 to be left standing (forexample, the noise level in the vicinity of 4.2 MHz was measured, whilerotating the optical information recording medium 1 at a linear velocityof 5.3 m/s). Based on the results of the measurement, the degree ofnoise-causing deterioration was calculated.

In this case, as shown in FIG. 2, when Mg is not added to the materialfor forming the second sub-recording film 4 b, which contains Cu as themain component (when Mg is added in an amount of 0 at %), the degree ofnoise-causing deterioration is 6.5 dB, whereas when Mg is added to thematerial containing Cu as the main component in an amount of 5 at %, thedegree of noise-causing deterioration is decreased to 0.9 dB.Furthermore, when Mg is added in amounts of 10 at %, 15 at %, 21 at %,39 at %, and 49.5 at %, the degree of noise-causing deterioration islowered to 0.4 dB, 0.7 dB, 1.1 dB, 0.9 dB, and 1.4 dB, respectively.Therefore, by adding Mg to the material containing Cu as the maincomponent in an amount not less than 5 at % and less than 50 at %, it ispossible to reduce the degree of noise-causing deterioration to a levelof 1.5 dB or lower.

Further, the present inventors have confirmed that the degradation ratioof reflectance is decreased by adding Mg to the material containing Cuas the main component. More specifically, the optical informationrecording medium 1 was left standing e.g. for 50 hours in theenvironment of 80 degree Celsius and 85% RH, and the degree ofdegradation of reflectance (degradation ratio: [reflectance before themedium 1 was left standing—reflectance after the medium 1 was leftstanding]/reflectance before the medium 1 was left standing) wasmeasured before and after the medium 1 was left standing. In this case,as shown in FIG. 3, when Mg is not added to the material for forming thesecond sub-recording film 4 b, which contains Cu as the main component,the degradation ratio is 27%, whereas when Mg is added to the materialcontaining Cu as the main component in an amount of 5 at %, thedegradation ratio is decreased to 21%. Furthermore, when Mg is added inamounts of 10 at %, 15 at %, 21 at %, 39 at %, and 49.5 at %, thedegradation ratio of reflectance is lowered to 13%, 7%, 2%, 3%, and4.5%, respectively. Therefore, by adding Mg to the material containingCu as the main component in an amount not less than 5 at % and less than50 at %, it is possible to suppress the degradation of reflectance,thereby making it possible to store record data for a long time period.Further, by adding Mg to the material containing Cu as the maincomponent in an amount not less than 15 at % and less than 50 at %, itis possible to further suppress the degradation of reflectance, therebymaking it possible to store record data for a long time period.

In the above examples, the reason for larger values of the degree ofnoise-causing deterioration exhibited when no Mg was added is presumablydue to significant corrosion of Cu contained in the second sub-recordingfilm 4 b as the main component. Therefore, by forming the secondsub-recording film 4 b using the material containing Cu as the maincomponent and having Mg added in an amount not less than 5 at % and lessthan 50 at %, it is possible to manufacture the optical informationrecording medium 1 capable of normally reproducing recorded data(reducing the noise level), and storing the record data for a long timeperiod (decreasing the degree of noise-causing deterioration and thedegradation ratio of reflectance). Furthermore, if the amount of Mgadded is defined to be not less than 15 at % and less than 50 at %, itis possible to more positively prevent the degradation of reflectance,thereby making it possible to realize reliable storage of record datafor a long time period.

Next, a description will be given of the relationship between thethickness (layer thickness) of the recording layer 4 and the C/N ratio.

As described above, by reducing the layer thickness of the recordinglayer 4 (the sum of the thickness of the first sub-recording film 4 aand the thickness of the second sub-recording film 4 b), it is possibleto enhance the smoothness of the upper surfaces of the first and secondsub-recording films 4 a and 4 b, thereby making it possible to increasethe C/N ratio. However, when the layer thickness of the recording layer4 is too small, the amount of change in optical characteristics of therecording layer 4 before and after recording of data thereon becomes toosmall, causing a reduced C/N ratio. This makes it difficult to normallyreproduce record data. On the other hand, when the layer thickness ofthe recording layer 4 is too large, a crack can be produced in theoptical information recording medium 1 due to internal stresses of thefirst and second sub-recording films 4 a and 4 b, and the smoothness ofthe upper surfaces of the first and second sub-recording films 4 a and 4b is reduced to increase the noise level, which results in the reducedC/N ratio. Further, when the layer thickness of the recording layer 4 istoo large, the recording sensitivity of the recording layer 4 can belowered. Therefore, it is required to define the layer thickness of therecording layer 4 in view of such circumstances.

More specifically, when the layer thickness of the recording layer 4 isless than 2 nm, or when the layer thickness thereof is more than 40 nm,the C/N ratio is excessively decreased to make it difficult to normallyreproduce record data. On the other hand, when the layer thickness ofthe recording layer 4 is not less than 5 nm and not more than 20 nm, theC/N ratio becomes a relatively large value, which makes it possible toperform reliable reproduction of record data. In this case, when thelayer thickness of the recording layer 4 is less than 2 nm, the opticalcharacteristics of the recording layer 4 are hardly changed betweenbefore and after recording of data on the recording layer 4, so that theC/N ratio is decreased. Further, when the layer thickness of therecording layer 4 is more than 40 nm, the smoothness of the uppersurfaces of the first and second sub-recording films 4 a and 4 b isreduced, resulting in the increased noise level, and the reduced C/Nratio. Furthermore, when the layer thickness of the recording layer 4 ismore than 40 nm, a crack is produced in the recording layer 4 due to theinternal stresses of the first and second sub-recording films 4 a and 4b, when the optical information recording medium 1 is heated or cooled,or when a force for bending the medium 1 is applied to the medium 1.Additionally, it has also been confirmed that when the layer thicknessof the recording layer 4 is more than 40 nm, the recording sensitivityof the recording layer 4 is reduced. Therefore, to reliably reproducerecord data while preventing production of a crack and reduction of therecording sensitivity, it is preferable to form the first sub-recordingfilm 4 a and the second sub-recording film 4 b such that the layerthickness of the recording layer 4 is not less than 2 nm and not morethan 40 nm. Further, to more reliably reproduce record data, it ispreferable to form the first sub-recording film 4 a and the secondsub-recording film 4 b such that the layer thickness of the recordinglayer 4 is not less than 5 nm and not more than 20 nm.

As described hereinabove, according to the optical information recordingmedium 1, the first sub-recording film 4 a is formed by using the firstmaterial containing Si as the main component, and the secondsub-recording film 4 b is formed in the vicinity of the firstsub-recording film 4 a by using the second material containing Cu as themain component and having Mg added thereto. The addition of Mg makes itpossible to reduce the degree of noise-causing deterioration (suppress arise in the noise level due to aging), and greatly improve thedegradation ratio of reflectance (suppress a decrease in reflectance).Consequently, it is possible to perform high-density recording of recorddata, and store the recorded data for a long time period such that therecorded data can be normally reproduced during the long time period.Further, the addition of Mg makes it possible to improve the smoothnessof the upper surface of the second sub-recording film 4 b, therebysignificantly lowering the noise level. Therefore, the C/N ratio can beenhanced, whereby record data can be reliably reproduced. Furthermore,the recorded portions M can be positively formed in the recording layer4even when the laser beam L small in power is irradiated.

According to the optical information recording medium 1, the secondsub-recording film 4 b is formed by using the second material having Mgadded thereto in an amount not less than 5 at % and less than 50 at %,whereby it is possible to decrease the degree of noise-causingdeterioration to a level 1.5 dB or lower, and reduce the degradationratio of reflectance to a value of 21% or less. This makes it possibleto provide the optical information recording medium 1 capable ofreliably storing record data for a long time period.

Furthermore, according to the optical information recording medium 1, ifthe second sub-recording film 4 b is formed by using the second materialhaving Mg added thereto in an amount not less than 15 at % and less than50 at %, it is possible to reduce the degradation ratio of reflectanceto a value 7% or less. This makes it possible to provide the opticalinformation recording medium 1 capable of more reliably storing recorddata for a long time period.

Further, according to the optical information recording medium 1, therecording layer 4 is constructed by forming the first sub-recording film4 a and the second sub-recording film 4 b such that they are in contactwith each other, whereby when the laser beam L adjusted to the recordingpower is irradiated to the recording layer, the first sub-recording film4 a and the second sub-recording film 4 b can be easily mixed with eachother to thereby form the recorded portions M.

Still further, according to the optical information recording medium 1,the light transmitting layer 6 is formed in a manner covering therecording layer 4, whereby it is possible to positively prevent thefirst dielectric layer 5 a, the recording layer 4, and so forth, frombeing scratched.

Further, according to the optical information recording medium 1, therecording layer 4 is formed by the second sub-recording film 4 b and thefirst sub-recording film 4 a, sequentially deposited on the substrate 2in the mentioned order, such that record data can be recorded andreproduced by irradiation of the laser beam L to the recording layer 4from the light transmitting layer 6 side. Therefore, the lighttransmitting layer 6 can be formed to have a thickness less than that ofthe substrate 2, so that even when a pickup having an objective lenswith a large numerical aperture (NA) is used, a sufficiently large tiltmargin can be secured. Further, in the construction adapted toirradiation of the laser beam L to the recording layer 4 from the lighttransmitting layer 6 side, the present optical information recodingmedium can more reliably form the recorded portions M in the recordinglayer 4 even with the laser beam L relatively small in power, than anoptical information recording medium in which the recording layer 4 isformed by the first sub-recording film 4 a and the second sub-recordingfilm 4 b, sequentially deposited on the substrate 2 in the mentionedorder.

Furthermore, according to the optical information recording medium 1,the first dielectric layer 5 a is formed between the recording layer 4and the light transmitting layer 6, and the second dielectric layer 5 bis formed between the substrate 2 and the recording layer 4, whereby itis possible to prevent thermal deformations of the substrate 2 and thelight transmitting layer 6 during irradiation of the laser beam L(during formation of the recorded portions M). As a result, it ispossible to positively prevent a rise in the noise level caused by thethermal deformations. Further, since corrosion of the recording layer 4can be prevented, it is possible to store recorded data for a long timeperiod such that the recorded data can be normally reproduced during thelong time period.

Furthermore, according to the optical information recording medium 1,the reflective layer 3 is formed between the substrate 2 and the seconddielectric layer 5 b, whereby the effect of multi-beam interference isfurther increased. This makes it possible to further increase thedifference in optical reflectance between the recorded portions M andthe unrecorded portions, whereby it is possible to more reliablyreproduce record data.

Next, an optical information recording medium 1A according to anotherembodiment of the present invention will be described with reference toFIG. 4. It should be noted that in the following description, thecomponent parts and elements identical to those of the aforementionedoptical information recording medium 1 are designated by identicalreference numerals, and duplicate description thereof is omitted.

As shown in FIG. 4, the optical information recording medium 1A iscomprised of a first dielectric layer 5 a, a recording layer 4, a seconddielectric layer 5 b, a reflective layer 3, and a protective layer 6A,sequentially deposited on the substrate 2A in the mentioned order. Inthis case, the optical information recording medium 1A is configuredsuch that record data can be recorded and reproduced by irradiation of alaser beam L to the recording layer 4 from the substrate side.Therefore, the substrate 2A is made of a resin material having a lighttransmitting property (e.g. a polycarbonate resin) by the injectionmolding method such that it has a thickness not less than 0.5 mm and notmore than 1.3 mm (e.g. approximately 0.6 mm), and that the laser beam Lcan be transmitted therethrough. It should be noted that the materialfor forming the substrate 2A is only required to be capable oftransmitting the laser beam L.

The recording layer 4 is comprised of a first sub-recording film 4 a(first recording film) and a second sub-recording film 4 b (secondrecording film), sequentially deposited on the first dielectric layer 5a in the mentioned order. It should be noted that materials for formingthe first sub-recording film 4 a and the second sub-recording film 4 b,methods for forming them, thicknesses thereof are similar to thosedescribed in detail hereinabove with respect to the first sub-recordingfilm 4 a and the second sub-recording film 4 b of the opticalinformation recording medium 1, and hence description thereof isomitted. The protective layer 6A prevents the recording layer 4, thesecond dielectric layer 5 b, and so forth, from being scratched, and isformed e.g. of a resin material, such as an ultraviolet-curing resin oran electron beam-curing resin, such that it has a thickness not lessthan 1 μm and not more than 100 μm (e.g. approximately 7 μm). In thiscase, when the protective layer 6A has a thickness of less than 1 μm, itbecomes difficult to protect the recording layer 4 and the seconddielectric layer 5 b, whereas when the light transmitting layer 6 has athickness of more than 100 μm, it becomes difficult to form theprotective layer 6A such that it is uniform in thickness. To form theprotective layer 6A, there can be employed a method of applying a resinmaterial by the spin coating method or the like, and then curing thesame.

Similarly to the optical information recording medium 1 describedhereinabove, in the optical information recording medium 1A, when thelaser beam L adjusted to a recording power is irradiated to therecording layer 4, an element (Si, in the present case), which is themain component of the first sub-recording film 4 a, and an element (Cu,in the present case), which is the main component of the secondsub-recording film 4 b, are mixed with each other, and as shown in FIG.4, to form recorded portions M. It should be noted that although FIG. 4shows a state of an area irradiated with the laser beam L, in which thefirst sub-recoding film 4 a and the second sub-recording film 4 b aretotally mixed in the direction of thickness to form the recoded portionsM, it is also possible to form the recorded portions M such that recorddata can be normally reproduced therefrom (such that the record data issufficiently readable), even if the first and second sub-recording films4 a and 4 b are partially mixed with each other in the vicinity of theinterface therebetween. In this case, in the optical informationrecording medium 1A, Mg is added to the material (material containing Cuas the main component) used for forming the second sub-recording film 4b, and hence the degree of noise-causing deterioration and thedegradation ratio of reflectance are decreased compared with a case inwhich the second sub-recording film 4 b is formed by using a materialhaving no Mg added thereto.

Further, since the first sub-recording film 4 a and the secondsub-recording film 4 b are sequentially deposited on the substrate 2A inthe mentioned order, the recorded portions M are more reliably formed(record data is more reliably recorded) in the recording layer4 evenwith the laser beam L relatively small in power, than when the recordinglayer 4 is formed by the second sub-recording film 4 b and the firstsub-recording film 4 a, sequentially deposited on the substrate 2A inthe mentioned order. Furthermore, the recording layer 4 is sandwiched bythe first dielectric layer 5 a and the second dielectric layer 5 b, andhence even when the first sub-recording film 4 a and the secondsub-recording film 4 b are heated by the irradiation of the laser beam Lto such an extent that they are mixed with each other, it is possible toprevent thermal deformations of the substrate 2 and the like. This makesit possible to prevent a rise in the noise level, a decrease in the C/Nratio, and deterioration of jitter characteristics.

As described above, according to the optical information recordingmedium 1A, the recording layer 4 is formed by the first sub-recordingfilm 4 a and the second sub-recording film 4 b, sequentially depositedon the substrate 2A in the mentioned order, such that record data can berecorded and reproduced by irradiation of the laser beam L to therecording layer 4 from the substrate 2A side. Since the secondsub-recording film 4 b is formed by using the material having Mg addedthereto, it is possible to reduce the degree of noise-causingdeterioration (suppress a rise in the noise level due to aging), andgreatly improve the degradation ratio of reflectance (suppress adecrease in reflectance) Consequently, it is possible to performhigh-density recording of record data, and store the recorded data for along time period such that the recorded data can be normally reproducedduring the long time period. In this case, in the construction adaptedto irradiation of the laser beam L to the recording layer 4 from thesubstrate 2A side, the first sub-recording film 4 a and the secondsub-recording film 4 b are sequentially deposited on the substrate 2A inthe mentioned order, so that the recorded portions M can be morereliably formed in the recording layer4 even with the laser beam Lrelatively small in power, than when the recording layer 4 is formed bythe second sub-recording film 4 b and the first sub-recording film 4 a,sequentially deposited on the substrate 2A in the mentioned order.

Further, according to the optical information recording medium 1A, thefirst dielectric layer 5 a is formed between the substrate 2A and therecording layer 4, and the second dielectric layer 5 b is formed betweenthe recording layer 4 and the protective layer 6A, whereby it ispossible to prevent thermal deformations of the substrate 2A and thelike during irradiation of the laser beam L (during formation of therecorded portions M). As a result, it is possible to positively preventa rise in the noise level caused by the thermal deformations. Further,since corrosion of the recording layer 4 can be prevented, it ispossible to store recorded data for a long time period in a manner suchthat the data can be normally reproduced.

Furthermore, according to the optical information recording medium 1A,the reflective layer 3 is formed between the second dielectric layer 5 band the protective layer 6A, whereby the effect of multi-beaminterference is further increased. This makes it possible to furtherincrease the difference in optical reflectance between the recordedportions M and unrecorded portions, whereby it is possible to morereliably reproduce record data.

It should be noted that the present invention is by no means limited tothe aforementioned embodiments. For example, although in theabove-described embodiments, the description has been given of theexamples in which the first sub-recording film 4 a and the secondsub-recording film 4 b are arranged adjacent to each other in thedirection of thickness of the optical information recording medium 1 or1A, this is not limitative, but the construction of the recording layer4 can be changed as required, so long as it is configured to be capableof forming an area for mixing the first sub-recording film 4 a and thesecond sub-recording film 4 b with each other when the laser beam Ladjusted to the recording power is irradiated to the recording layer 4.More specifically, for example, the recording layer 4 can also be formedby interposing one or more very thin dielectric layers or the likebetween the first sub-recording film 4 a and the second sub-recordingfilm 4 b, or alternatively it can be formed by interposing a layer madeof a mixture of materials for forming the first sub-recording film 4 aand the second sub-recording film 4 b, between the sub-recording films 4a and 4 b. Further, although in the above-described embodiments, thedescription has been given, by way of example, of the opticalinformation recording medium 1 or 1A which includes the recording layer4 comprised of two recording films, i.e. the first sub-recording film 4a and the second sub-recording film 4 b, this is not limitative, but therecording layer according to the present invention can be configured tohave not only the sub-recording films 4 a and 4 b but also one or moresub-recording films which are formed of a material containing an elementselected from the group consisting of Si, Ge, C, Sn, Zn, and Cu, as themain component.

Further, although in the above-described embodiments, the descriptionhas been given of the optical information recording medium 1 which hasthe first sub-recording film 4 a corresponding to the first recordingfilm in the present invention formed toward i.e. closer to the lighttransmitting layer 6, and the second sub-recording film 4 bcorresponding to the second recording film in the present inventionformed toward i.e. closer to the substrate 2, and the opticalinformation recording medium 1A, which has the first sub-recording film4 a corresponding to the first recording film in the present inventionformed toward the substrate 2A, and the second sub-recording film 4 bcorresponding to the second recording film in the present inventionformed toward the protective layer 6A, this is not limitative, but inthe construction adapted to irradiation of the laser beam L from thelight transmitting layer side, it is possible to construct the opticalinformation recording medium by forming the second sub-recording film 4b toward i.e. closer to the light transmitting layer 6, and the firstsub-recording film 4 a toward i.e. closer to the substrate 2, or in theconstruction adapted to irradiation of the laser beam L from thesubstrate 2A side, it is possible to construct the optical informationrecording medium by forming the second sub-recording film 4 b towardi.e. closer to the substrate 2A, and the first sub-recording film 4 atoward i.e. closer to the protective layer 6A.

Further, although in the above-described embodiments, the descriptionhas been given of the optical information recording media 1 and 1A,including the first dielectric layer 5 a and the second dielectric layer5 b, this is not limitative, but the optical information recordingmedium according to the present invention encompasses opticalinformation recording media which do not have one or any of the firstdielectric layer 5 a and the second dielectric layer 5 b. Furthermore,although in the above-described embodiments, the description has beengiven of the optical information recording media 1 and 1A, including thereflective layer 3, this is not limitative, but the optical informationrecording medium according to the present invention encompasses opticalinformation recording media which do not have the reflective layer 3.Further, although in the above-described embodiments, the descriptionhas been given of the example in which record data is recorded andreproduced by using the blue-violet laser beam L having a wavelength (λ)not less than 380 nm and not more than 450 nm (e.g. 405 nm), this is notlimitative, but the optical information recording medium according tothe present invention can be configured such that it is capable ofrecording and reproducing record data using various laser beams having awavelength (λ) not less than 250 nm and not more than 900 nm.Furthermore, although in the above-described embodiments, thethicknesses of the respective layers are described only by way ofexamples, and this is not limitative, but of course they can be changedas required.

1. An optical information recording medium for recording and reproducingrecord data, comprising: a substrate; and a recording layer formed onthe substrate, for having a laser beam irradiated thereto for recordingand reproduction of the record data, the recording layer including afirst recording film formed of a first material containing Si as a maincomponent, and a second recording film formed of a second materialcontaining Cu as a main component and having Mg added thereto, thesecond recording film being formed in the vicinity of the firstrecording film; wherein the substrate is formed to be capable oftransmitting the laser beam therethrough, the recording layer beingformed by the first recording film and the second recording film,sequentially deposited on the substrate in the mentioned order, theoptical information recording medium being configured such that therecord data can be recorded and reproduced by irradiation of the laserbeam to the recording layer from a substrate side.
 2. An opticalinformation recording medium as claimed in claim 1, wherein the secondmaterial has Mg added thereto in an amount not less than 5 at % and lessthan 50 at %.
 3. An optical information recording medium as claimed inclaim 2, wherein the second material has Mg added thereto in an amountnot less than 15 at % and less than 50 at %.
 4. An optical informationrecording medium as claimed in claim 1, wherein the recording layer isconfigured such that the first and second recording films are in contactwith each other.
 5. An optical information recording medium as claimedin claim 1, including a protective layer formed in a manner covering therecording layer.
 6. An optical information recording medium as claimedin claim 5, wherein the protective layer is formed to be capable oftransmitting the laser beam therethrough, the recording layer beingformed by the second recording film and the first recording film,sequentially deposited on the substrate in the mentioned order, theoptical information recording medium being configured such that therecord data can be recorded and reproduced by irradiation of the laserbeam to the recording layer from a protective layer side.
 7. An opticalinformation recording medium as claimed in claim 6, including a firstdielectric layer formed between the recording layer and the protectivelayer, and a second dielectric layer formed between the substrate andthe recording layer.
 8. An optical information recording medium asclaimed in claim 7, including a reflective layer formed between thesubstrate and the second dielectric layer.
 9. An optical informationrecording medium as claimed in claim 1, including a first dielectriclayer formed between the substrate and the recording layer, and a seconddielectric layer formed between the recording layer and the protectivelayer.
 10. An optical information recording medium as claimed in claim9, including a reflective layer formed between the second dielectriclayer and the protective layer.